Automatic transmissions, especially for motor vehicles, comprise planetary sets shifted by means of frictional or shifting elements, according to the prior art, such as clutches and brakes and usually connected with a starting element like a hydrodynamic torque converter or a fluid clutch subject to slip action and optionally provided with a bridge clutch.
One such transmission results from EP 0 434 525 A1. It essentially comprises one input shaft and one output shaft disposed in parallel, one double planetary gear set situated concentrically to the output shaft and five shifting elements in the form of three clutches and two brakes, the selective locking of which by pairs determines the different gear ratios between the input shaft and the output shaft.
Also known from the Applicant's DE 199 49 507 A1 is a multiple gear transmission where on the input shaft two non-shiftable front-mounted gear sets are provided which produce the output side two rotational speeds which together with the rotational speed of the input shaft can optionally be shifted by selective closing of the shifting elements used to a shiftable double planetary gear set acting upon the output shaft in a manner such that for changing from one gear to the respective higher or lower gear that follows, only one shifting element of the two just actuated shifting elements has to be engaged or disengaged.
There has also been disclosed within the scope of EP 0 434 525 A1 one multiple gear transmission containing one input shaft and one output shaft located in one housing, one planetary set concentric with the output shaft and consisting of four elements designated from one first to one fourth in order of rotational speed, that is, one so-called double planetary set and five shifting elements, namely, three clutches and two brakes, the selective engagement of which by pairs determines different reduction ratios between input shaft and the output shaft, the transmission having two power paths so that by the selective engagement by pairs of the five shifting elements six forward gears are achieved.
DE 199 10 299 C1 has disclosed a planetary gear variable transmission having three transmission elements where one input shaft can be brought to driving connection with one output shaft by at least one of three planetary gear transmission elements. In the known planetary gear variable transmission, by using each time three frictional-engagement clutches and brakes, it is possible to shift five forward gears including one direct gear having a predetermined ratio.
In the known planetary gear variable transmission, it is possible by interrupting a specific driving connection between two of the three transmission elements, to provide an added sixth forward gear. In another embodiment, this is accomplished by additional auxiliary planets and by an added outer auxiliary central gear that meshes with the latter and by an additional brake can be decelerated in the sixth forward gear. In the other embodiments, the auxiliary central gear makes still one seventh forward gear and one additional reverse gear possible.
The problem on which this invention is based is to propose a multiple gear transmission of the kind mentioned above where the construction cost is optimized and, in addition, the effectiveness in the main driving gears is improved with regard to the towing and toothing losses.